Converter circuit and motor drive control apparatus, air-conditioner, refrigerator, and induction heating cooker provided with the circuit

ABSTRACT

A converter circuit capable of being compact and light-weight and capable of reducing switching loss, a motor drive control apparatus, an air-conditioner, a refrigerator, and an induction heating cooker provided with the circuit. The converter circuit including: a step-up converter including a rectifier, a step-up reactor, a switching element, and a reverse current prevention element; a step-up converter having a step-up reactor, a switching element, and a reverse current prevention element and connected in parallel with the step-up converter; switching control unit that controls switching elements; and a smoothing capacitor that is provided at the output of the step-up converters. The switching control unit switches the current mode of the current flowing through the step-up reactors into any of a continuous mode, a critical mode, and a discontinuous mode based on a predetermined condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of prior application Ser.No. 13/058,401 filed Feb. 10, 2011, which is a National Stage ofApplication No. PCT/JP2009/055109 filed Mar. 17, 2009, the entirecontents of each of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a converter circuit and a motor drivecontrol apparatus, an air-conditioner, a refrigerator, and an inductionheating cooker provided with the circuit.

BACKGROUND ART

Conventionally, a step-down converter and a step-up/step-down converteras well as a step-up converter are usually used as a power factorcorrection (PFC) circuit.

In order to achieve a small and light-weighted converter circuit, aconverter circuit is proposed including “a rectification circuit whoseinput is an AC power source, a first step-up converter circuit connectedto the output of the rectification circuit and having at least a firstreactor, first switching means and a first diode, a second step-upconverter circuit connected to the first step-up converter circuit inparallel and having at least a second reactor, second switching meansand a second diode, and a smoothing capacitor connected to outputs ofthe first step-up converter circuit and the second step-up convertercircuit.” (For example, refer to Patent Literature 1)

-   Patent Literature 1: Japanese Patent No. 2008-86107 (claim 1)

SUMMARY OF INVENTION Technical Problem

When employing a step-up converter, or a step-down converter and astep-up/step-down converter as a power factor correction circuit, it isnecessary to operate a current flowing through a reactor as a continuousmode. Therefore, the reactor having a large inductance is needed and asmall and light-weighted circuit cannot be achieved disadvantageously.

With a configuration in which a plurality of systems of a convertercircuit is connected in parallel, switching loss becomes largedisadvantageously.

The present invention is made to solve the above-mentioned problems andits object is to provide a small light-weighted converter circuitcapable of reducing switching loss and a motor drive control apparatus,an air-conditioner, a refrigerator, and an induction heating cookerhaving the circuit.

Solution to Problem

The converter circuit according to the present invention includes arectifier to rectify AC voltages, a first converter section that isconnected with the output of the rectifier and has a first reactor, afirst switching element, and a first reverse current prevention element,a second converter section that is connected with the output of therectifier, that has a second reactor, a second switching element, and asecond reverse current prevention element, and that is connected inparallel to the first converter section, switching control means thatcontrols the first and the second switching elements, and a smoothingcapacitor provided at the output of the first and the second convertersections. The switching control means switches the current mode of thecurrent flowing through the first and the second reactors into any of acontinuous mode, a critical mode, and a discontinuous mode based on apredetermined condition.

Advantageous Effects of Invention

Since the present invention includes a first converter section and asecond converter section connected with the first converter section inparallel, an inductance required for a reactor can be made small,allowing to achieve a small light-weighted reactor.

Switching loss can be reduced because a current mode of the currentflowing through the first and the second reactors can be switched to anyof a continuous mode, a critical mode, and a discontinuous mode based ona predetermined condition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a converter circuit according toEmbodiment 1 of the present invention.

FIG. 2 is a diagram showing an electric signal and a current waveform ofeach part at a continuous mode operation of the converter circuit.

FIG. 3 is a diagram showing the electric signal and the current waveformof each part at a discontinuous mode operation of the converter circuit.

FIG. 4 is a diagram showing the electric signal and the current waveformof each part at a critical mode operation of the converter circuit.

FIG. 5 is a configuration diagram of the converter circuit according toEmbodiment 2 of the present invention.

FIG. 6 is a diagram illustrating the current waveform of the convertercircuit.

FIG. 7 is a diagram illustrating switching operation of a current modeaccording to Embodiment 2 of the present invention.

FIG. 8 is a configuration diagram of the converter circuit according toEmbodiment 2 of the present invention.

FIG. 9 is a configuration diagram of the converter circuit according toEmbodiment 3 of the present invention.

FIG. 10 is a configuration diagram of the converter circuit according toEmbodiment 4 of the present invention.

FIG. 11 is a configuration diagram of the converter circuit according toEmbodiment 4 of the present invention.

FIG. 12 is a configuration diagram of a motor drive circuit according toEmbodiment 6 of the present invention.

FIG. 13 is a configuration diagram of an air-conditioner according toEmbodiment 7 of the present invention.

FIG. 14 is a configuration diagram of a refrigerator according toEmbodiment 8 of the present invention.

FIG. 15 is a configuration diagram of an induction heating cookeraccording to Embodiment 9 of the present invention.

FIG. 16 is a diagram showing a configuration of a step-down converterand a step-up/step-down converter.

REFERENCE SIGNS LIST

-   1 commercial power supply-   2 rectifier-   2 a-2 d rectifying diode-   3 a-3 c step-up converter-   4 a-4 c step-up reactor-   5 a-5 c switching element-   6 a-6 c reverse current prevention element-   7 switching control means-   8 smoothing capacitor-   9 a, 9 b opening and closing means-   10 load-   11 inverter circuit-   11 a-11 f switching element-   12 motor-   13 load circuit-   14 induction heating coil-   15 resonance capacitor-   20 current detection means-   30 output power detection means-   40 opening and closing control means-   50 inverter drive means-   310 outdoor unit-   311 refrigerant compressor-   312 blower-   320 indoor unit-   400 refrigerator-   401 refrigerant compressor-   402 cooling compartment-   403 cooler-   404 blower

DESCRIPTION OF EMBODIMENTS Embodiment 1

FIG. 1 is a configuration diagram of a converter circuit according toEmbodiment 1 of the present invention.

In FIG. 1, a rectifier 2 that rectifies AC voltage of the commercialpower supply 1 is constituted by a bridge connection of four rectifyingdiodes 2 a-2 d. To the output of the rectifier 2, a step-up converter 3a, which is a first converter section, and a step-down converter 3 b,which is a second converter section, are connected in parallel.

The step-up converter 3 a is constituted by a step-up reactor 4 a, whichis a first reactor, a switching element 5 a, which is a first switchingelement composed of, for example, an IGBT (Insulated Gate BipolarTransistor), and a reverse current prevention element 6 a, which is afirst reverse current prevention means composed of such as a fastrecovery diode. The step-up converter 3 b is constituted by a step-upreactor 4 b, which is a second reactor, a switching element 5 b, whichis a second switching element composed of, for example, the IGBT, andthe reverse current prevention element 6 b, which is a second reversecurrent prevention element composed of, for example, the fast recoverydiode. Inductance values of the step-up reactors 4 a and 4 b arementioned later.

Switching of the switching elements 5 a and 5 b is controlled byswitching control means 7 and the output of the rectifier 2 is boosted.

Switching elements 5 a and 5 b are provided with a diode FWD (FreeWheeling Diode), which is connected in inverse-parallel, respectively.The diode prevents the switching element 5 from being broken caused by asurge generated when the switching element 5 turns off.

In the present embodiment, descriptions will be given to the case wherethe first and second converter sections are step-up converters 3 a and 3b, respectively. However, the present invention is not limited thereto.An arbitrary switching converter may be applied such as a step-upconverter, a step-down converter, and a step-up/step-down converter.

For example, as shown in FIG. 16( a), the step-down converter may beused for the first and the second converter sections. Alternatively, thestep-up/step-down converter may be used for the first and the secondconverter sections.

The output of the step-up converter 3 a and the step-up converter 3 b issmoothed by a smoothing capacitor 8. To the output of the step-upconverters 3 a and 3 b, a load (not shown) is connected and the smoothedoutput of the step-up converters 3 a and 3 b is applied.

Next, descriptions will be given to an inductance value of the step-upreactors 4 a and 4 b (hereinafter, simply referred to as a “step-upreactor 4” unless discriminated).

The inductance value L of the step-up reactor 4 configured as the aboveis defined by formula 1 as follows.

$\begin{matrix}{L = {\frac{V_{in}^{2}}{\sqrt{2}{P_{in} \cdot K \cdot f_{c}}} \cdot \frac{V_{o} - {\sqrt{2}V_{in}}}{V_{o}}}} & {{Formula}\mspace{14mu} 1}\end{matrix}$

where, fc is a switching frequency, Vin an input voltage, Vo an outputvoltage, Pin an input power ripple rate, and K a current ripple rate.

As shown by Formula 1, the larger the current ripple rate K of thecurrent flowing through the step-up reactor 4, the smaller theinductance value L. Accordingly, since by making the current flowingthrough the step-up reactor 4 to be the peak critical mode ordiscontinuous mode (to be mentioned later), the current value becomeslarger than the average current value to increase the current ripplerate K, the inductance value L required for the step-up reactor 4 can bemade small. Hence, the value obtained from the above Formula 1 is usedfor the inductance value L of the step-up reactor 4 when the currentflowing through the step-up reactor 4 is made to be the critical mode orthe discontinuous mode.

Descriptions will be given to the behavior and operation of theconverter circuit configured above as follows.

As shown in FIG. 1, the AC voltage of the commercial power supply 1 isrectified by the rectifier 2. The output of the rectifier 2 is branchedinto two current paths by the step-up converters 3 a and 3 b connectedin parallel. The branched current flows through the step-up reactors 4 aand 4 b. Switching of the switching elements 5 a and 5 b is controlledby switching control means 7 and the output of the rectifier 2 isboosted. The switching control means 7 controls switching of theswitching elements 5 a and 5 b to control a current mode and a phasedifference of the current flowing into the step-up reactors 4 a and 4 b.The switching operation will be mentioned later.

FIG. 2 is a diagram showing an electric signal and a current waveform ofeach part at a continuous mode operation of the converter circuit. FIG.3 is a diagram showing an electric signal and a current waveform of eachpart at a discontinuous mode operation of the converter circuit. FIG. 4is a diagram showing an electric signal and a current waveform of eachpart at a critical mode operation of the converter circuit.

Next, switching operation of the step-up converters 3 a and 3 b will beexplained.

When the switching element 5 a turns on in the step-up converter 3 a,conduction of a reverse current prevention element 6 a is suspended andrectified voltage by the rectifier 2 is applied to the step-up reactor 4a. On the other hand, when the switching element 5 a turns off, thereverse current prevention element 6 a is made to conduct electricityand a reversed voltage is induced in the step-up reactor 4 a to when theswitching element 5 a turns on.

Thus, the current flowing through the step-up reactor 4 a linearlyincreases when the switching element 5 a turns on and linearly decreaseswhen the switching element 5 a turns off.

In the step-up converter 3 b, the current flowing through the step-upreactor 4 b linearly increases when the switching element 5 b turns onand linearly decreases when the switching element 5 b turns off as well.

In the switching operation of the switching elements 5 a and 5 b(hereinafter, simply referred to as “switching element 5” unlessdiscriminated) as shown in FIG. 2, the operation condition in which thecurrent flowing through the step-up reactor 4 does not become 0 (zero)even if being reduced, is called a continuous mode. On the other hand,as shown in FIG. 3, the operation condition, in which an interval existswhere the current flowing through the step-up reactor 4 decreases to 0(zero), is called a discontinuous mode. The operation condition, inwhich the switching element 5 turns on at the moment when the currentflowing through the step-up reactor 4 decreases to 0 (zero) while theswitching element 5 turns off, is called a critical mode from a meaningthat it is a boundary between the continuous mode and the discontinuousmode.

As mentioned above, the inductance value L of the step-up reactor 4employs a value defined when the current flowing through the step-upreactor 4 is made to be the critical mode or the discontinuous mode. Asshown in FIGS. 4 and 3, switching of the switching elements 5 a and 5 bis controlled by the switching control means 7 such that the currentflowing through the step-up reactors 4 a and 4 b becomes the criticalmode or the discontinuous mode.

The switching control means 7 controls the current flowing through thestep-up reactors 4 a and 4 b with a phase shift so that a predeterminedphase difference is created (for example, a phase difference of 180degrees constant, respectively) as shown in FIGS. 3 and 4.

Thus, while the input currents before being branched into two currentpaths by the step-up converters 3 a and 3 b that have operated as thecritical mode or the discontinuous mode in each step-up reactors 4 a and4 b, respectively are added to operate as the continuous mode.

As mentioned above in the present embodiment, the step-up converter 3 ismade to have two systems and operated such that the current flowing eachstep-up reactor 4 becomes the critical mode the critical mode or thediscontinuous mode. Therefore, two components are necessary thatconstitutes each step-up converter 3. However, since the current flowingthrough the step-up reactor 4 has a large current ripple against theaverage current value, the inductance value L required for the step-upreactor 4 can be made small, achieving the step-up reactor 4 to be smalland light-weighted.

Thereby, material cost of the step-up reactor 4 itself can be reduced,wiring can be reduced by making step-up reactor 4 on-board, andnoise-resistance can be improved.

Compared with a single system step-up converter 3, the small step-upreactor 4 can be provided by dividing itself into two, allowing designintending to improve degree-of-freedom of installing components in thecircuit, to improve assembling efficiency, and to reduce mistakes.

Further, by making the step-up reactor 4 occupying a greater part ofcircuitry capacity small and light-weighted, it becomes possible toreinforce merits such as to make the product itself small andlight-weighted.

By making the product itself small, it becomes possible to makepackaging of the relevant product light-weighted and small to achievereduction in packaging volume.

In the step-up converter 3, an FWD is provided in inverse-parallel tothe switching elements 5 a and 5 b. Because of this, the switchingelement 5 can be protected from breakdown caused by a surge generated inthe wiring impedance where one end of the step-up reactor 4, one end ofthe switching element 5, and one end of the reverse current preventionelement 6 are connected when the switching element 5 turns off.

Since the current flowing through the step-up reactor 4 is controlledwith phase shift, the input current can be operated in the continuousmode while each step-up reactor 4 is operated in the critical mode orthe discontinuous mode. Harmonics currents of the input current can besuppressed, resultantly.

When comparing with the single system step-up converter 3 in thediscontinuous mode or the critical mode, the current flowing througheach element of the step-up converter 3 is almost halved, therefore, asmall capacity element can be selected for the step-up reactor 4, theswitching element 5, and the reverse current prevention element 6.

As mentioned above, the input current is an addition of currents flowingthrough the step-up reactors 4 a and 4 b. Thereby, if the phasedifference of currents flowing the step-up reactors 4 a and 4 b iscontrolled by 180 degrees (reverse phase) in the switching control means7, the level of the current ripple of the input current becomes thesmallest, allowing to reduce high-frequency components of the inputcurrent. Then, the frequency of the current ripple of the input currentis twice the switching frequency.

A case is conceivable where the current ripple of the input currentcauses noises or vibrations at the doubled frequency of the switchingfrequency when controlling the phase difference by 180 degrees (reversephase). In this case, by controlling the phase difference of the currentflowing through the step-up reactors 4 a and 4 b to randomly vary withina predetermined range such as a random value around 180 degrees insteadof 180 degrees constant, the component of the doubled switchingfrequency can be reduced and the noise can be suppressed.

An example will be explained of method for generating a random value ofthe phase difference. Inside the switching control means 7, in the phasedifference difference calculation section (not shown) that obtainsrandom numbers in the range of, for example, −1 to 1 from a randomnumber generation section (not shown), a difference of the phasedifference is calculated by multiplying the maximum value 180 degrees ofthe difference of the phase difference by the random number. Here, byadding the difference to the phase difference 180 degrees, a randomnumber centering around 180 degrees is obtained as phase difference ofthe current flowing through the step-up reactors 4 a and 4 b.

Thereby, it becomes possible to suppress the current ripple, noises orvibrations dependent on the switching frequency without making eachswitching frequency of the switching elements 5 a and 5 b different.

When employing random numbers for the phase difference, some case isconceivable where the tone of noises is felt as if the level of thesound were totally increased from the sound having a rising peak. Then,by narrowing the range of the random number obtained from a randomnumber generation section, such as, −0.5 to 0.5 or −0.3 to 0.3, noiselevel and tone can be adjusted.

Embodiment 2

In Embodiment 1, operation is performed so that the current mode flowingthrough the step-up reactor 4 becomes the critical mode or thediscontinuous mode. In Embodiment 2, by switching the current modeduring operation, operation taking advantage of each current mode ispossible.

Here, descriptions will be given to characteristics of each currentmode.

When controlled by the continuous mode, the current ripple is smallerthan the critical mode and the discontinuous mode, allowing to suppressthe generation of harmonics components of the input current. On theother hand, the switching frequency becomes higher than the criticalmode and the discontinuous mode, causing a large switching loss in theswitching element 5 and the reverse current prevention element 6.

When operated in the critical mode, the current ripple rate becomessmaller than the discontinuous mode, enabling generation of thehigh-frequency components of the input current to be suppressed. On theother hand, the switching frequency becomes higher than thediscontinuous mode, causing a large switching loss in the switchingelement 5 and the reverse current prevention element 6.

When operated in the discontinuous mode, since the current ripple in theinput current is larger compared with the continuous mode and thecritical mode, suppressing effect of the harmonics components of theinput current is small. On the other hand, the switching frequencybecomes lower than the critical mode and the discontinuous mode, causinga small switching loss in the switching element 5 and the reversecurrent prevention element 6.

Thus, the switching control means 7 in Embodiment 2 switches the mode ofthe current flowing through the step-up reactors 4 a and 4 b into any ofthe continuous mode, the critical mode, and the discontinuous mode basedon a predetermined condition.

The predetermined condition to switch the current mode and concreteexamples will be explained.

Firstly, as the predetermined condition to switch the current mode,operation based on the input current will be explained.

FIG. 5 is a configuration diagram of the converter circuit according toEmbodiment 2 of the present invention.

In FIG. 5, the converter circuit further includes current detectionmeans 20 that detects the input current input to the step-up converters3 a and 3 b in addition to the configuration of the above Embodiment 1.

The other configuration is the same as that of Embodiment 1, and thesame signs will be given to the same configuration.

The inductance value L of the step-up reactor 4 employs the valuedefined by the above Formula 1 when the current flowing through thestep-up reactor 4 is in the critical mode. The critical mode is switchedto the discontinuous mode to be mentioned later. Therefore, it isnecessary to define the value L in the critical mode in which thecurrent ripple is smaller.

Based on the above configuration, the switching control means 7 switchesthe mode of the current flowing through the step-up reactor 4 based onthe magnitude (level) of the input current detected by current detectionmeans 20.

The switching control means 7 is set with 30% of the peak value of theinput current being a threshold, for example. When the magnitude (level)of the detected input current is equal to or larger than the threshold,switching of the switching element 5 is controlled so that the currentflowing through the step-up reactor 4 becomes the critical mode. On theother hand, when the magnitude (level) of the detected input current isless than the threshold, switching of the switching element 5 iscontrolled so that the current flowing through the step-up reactor 4becomes the discontinuous mode.

FIG. 6 is a diagram illustrating the current waveform of the convertercircuit. FIG. 7 is a diagram illustrating switching operation of thecurrent mode according to Embodiment 2 of the present invention.

In FIGS. 6 and 7, the current waveform and switching waveform of thestep-up reactor 4 a shown in FIG. 4 are expressed with the time axisbeing magnified. Waveforms shown in FIGS. 6 and 7 are typically shownfor expressing the switching operation, not being the actually measuredwaveforms. The switching frequency of the switching element 5 issubstantially shorter than that of the commercial power supply 1 (inputvoltage waveform).

As shown in FIG. 6, the current in the critical mode varies inproportion to the input voltage input to the step-up converter 3 a. Theswitching frequency becomes low in the vicinity of the peak of thecurrent and high in the vicinity of the zero cross point.

FIG. 7 shows the current waveform and switching waveform when thecurrent mode is switched based on the above operation. As shown in FIG.7, in the vicinity of the peak of the current, the operation becomes thecritical mode, and in the vicinity of the zero cross point thediscontinuous mode.

From the above operations, in the vicinity of the peak region where theinput current is large, the switching frequency becomes high comparedwith the discontinuous mode by making the current mode to be thecritical mode, however, contribution of the input current to thesuppression of harmonics components is large in the critical currentmode. Accordingly, the effect of suppressing the harmonics componentscan be maintained.

In the vicinity of the zero cross where the input current is small, whencompared with the critical mode, the effect of suppressing the harmonicscomponents becomes smaller by making the current to be the discontinuousmode, however, the switching loss can be decreased by reducing theswitching frequency.

In the above, explanations are given to the case where the threshold is30% of the input current, however, the present invention is not limitedthereto. For example, by setting the threshold larger such as 50% of theinput current, the range of the discontinuous mode can be expanded,allowing to reduce much more switching loss.

Further, by setting the threshold smaller such as 10% of the inputcurrent, the range of the critical mode can be expanded, allowing toreduce much more harmonics components of the input current.

Next, operation based on the switching frequency will be explained asthe predetermined condition to switch the current mode.

As shown in the above FIG. 6, in the operation of the critical mode, theswitching frequency cannot be kept constant, but being low in thevicinity of the peak of the input current and being high in the vicinityof the zero cross. Thus, switching control means 7 switches the mode ofthe current flowing through the step-up reactors 4 a and 4 b based onthe switching frequency of the switching element 5.

With the switching control means 7, a predetermined frequency is set asthe threshold in advance. In the switching control of the switchingelement 5, if the switching frequency is less than the threshold, themode of the current flowing through the step-up reactor 4 is switchedinto the critical mode. On the other hand, if the switching frequency isequal to or larger than the threshold, the mode of the current flowingthrough the step-up reactor 4 is switched into the discontinuous mode.

From the above operations, in the vicinity of the peak region where theswitching frequency is low, the switching frequency becomes highcompared with the discontinuous mode by making the current mode to bethe critical mode, however, contribution of the input current to thesuppression of harmonics components is large in the critical mode.Accordingly, the effect of suppressing the harmonics components can bemaintained.

In the vicinity of the zero cross where the switching frequency is high,when compared with the critical mode, the effect of suppressing theharmonics components becomes smaller, however, the switching loss can bedecreased by reducing the switching frequency.

If the threshold of the switching frequency set at the switching controlmeans 7 is made to conform to the specification of the switching element5, the switching element 5 can be prevented from breakdown and used inmore suitable environment.

Next, operation based on the output voltage will be explained as thepredetermined condition to switch the current mode.

In the operation of the critical mode, the higher the load, the lowerthe switching frequency for the output voltage. Thereby, the switchingcontrol means 7 switches the current mode flowing through the step-upreactor 4 based on the output voltage.

FIG. 8 is a configuration diagram of a converter according to Embodiment2 of the present invention.

In FIG. 8, the converter circuit is further provided with output powerdetection means 30 that detects the output power of the step-upconverters 3 a and 3 b in addition to the configuration of Embodiment 1.The other configurations are the same as that of Embodiment 1. The samesigns will be given to the same configurations.

Like FIG. 5, the inductance L of the step-up reactor 4 employs the valuedefined by the above formula 1 when the current flowing therethrough ismade to be the critical mode.

With the configuration above, the switching control means 7 switches thecurrent mode flowing through the step-up reactor 4 based on the outputvoltage detected by the output power detection means 30.

A predetermined output power is set at the switching control means 7 asthe threshold. When the detected output power is equal to or larger thanthe threshold, the switching element 5 is controlled such that thecurrent mode flowing through the step-up reactor 4 becomes the criticalmode. When the detected output power is less than the threshold, theswitching element 5 is controlled such that the current mode flowingthrough the step-up reactor 4 becomes the discontinuous mode.

From the above operations, in the case of high load, the switchingfrequency is high compared with the discontinuous mode by making thecurrent mode to be the critical mode, however, contribution of the inputcurrent to the suppression of harmonics components is large in thecritical current mode. Accordingly, the effect of suppressing thehigh-frequency components can be maintained.

In the case of low load, when compared with the critical mode, theeffect of suppressing the harmonics components becomes smaller by makingthe current mode to be the disconnection mode, however, the switchingloss can be decreased by reducing the switching frequency.

When providing a threshold with the above-mentioned input current andthe switching frequency, and the current mode is switched based on theoutput voltage like the above, since switching of the current mode isless frequent than the case where the current mode is frequentlyswitched within a time period of the power source, a simpler program canperform the control.

Next, descriptions will be given to operations based on the circuitefficiency as predetermined conditions for switching the current mode.

In the low-load area, the circuit efficiency improves with the increasein the output voltage. However, in the high-load area, the circuitefficiency sometimes decreases. Thereby, the switching control means 7switches the current mode flowing through the step-up reactor 4 based onthe circuit efficiency.

The converter circuit includes the current detection means 20 shown inthe above-mentioned FIG. 5 and the output power detection means 30 shownin the above-mentioned FIG. 8. The other configurations are the same asthat of Embodiment 1.

Based on the above-mentioned configuration, with the switching controlmeans 7, the predetermined circuit efficiency is set as the threshold.

The switching control means 7 obtains the circuit efficiency based onthe detected input current and the output power. Then, if the obtainedcircuit efficiency is less than the threshold, when the mode of thecurrent flowing through the step-up reactor 4 is the critical mode, itis switched into the discontinuous mode. When the continuous mode, it isswitched into the critical mode or the discontinuous mode.

Through the above-mentioned operations, when the circuit efficiency islowered, the switching frequency is reduced to decrease the switchingloss and the circuit efficiency can be improved.

Next, as the predetermined condition for switching the current mode,operations will be explained based on the output voltage, the outputvoltage command, or the changed values of the output voltage command.

When the output voltage command is changed against the step-up converter3, the ripple of the input current is changed. Therefore, the switchingcontrol means 7 switches the mode of the current flowing through thestep-up reactor 4 based on the output voltage, the output voltagecommand, of the changed values of the output voltage command.

Into the switching control means 7, information on the output voltagecommand that specifies the output voltage of the step-up converter 3 isinput. Then, the switching control means 7 controls the switchingelement 5 according to the input output voltage command to specify theoutput voltage of the step-up converter 3.

In the switching control means 7, a predetermined value or a range ispreset as a threshold, with which the current ripple becomes largeagainst the output voltage, the output voltage command, or the changedvalues of the output voltage. The other configurations are the same asthat of Embodiment 1.

For the inductance value L of the step-up reactor 4, a value defined bythe above formula 1 is employed when the current flowing through thestep-up reactor 4 is in the continuous mode. The object is to make itoperate in the continuous mode in which the current ripple is smaller.

Based on the above-mentioned configuration, the switching control means7 switches the mode of the current flowing through the step-up reactor 4into the continuous mode when the output voltage, the output voltagecommand, or the changed value of the output voltage command is thepredetermined value or in the region where the current ripple becomeslarge.

Through the above-mentioned operations, when the output voltage commandis changed and the current ripple becomes large, the current can beswitched into the continuous mode where the current ripple is smaller tobe able to suppress the harmonics component.

Embodiment 3

In the above-mentioned Embodiments 1 or 2, descriptions are given to thecase where the step-up converter has two systems. In Embodiment 3, theconverter of three or more systems will be employed.

FIG. 9 is a configuration diagram of the converter circuit according toEmbodiment 3 of the present invention.

As shown in FIG. 9, the converter circuit in Embodiment 3 includes thestep-up converter 3 c connected with the step-up converters 3 a and 3 bin parallel in addition to the configuration of Embodiment 1.

The step-up converter 3 c is constituted by the step-up reactor 4 c,which is the reactor of the present invention, and such as IGBT, aswitching element 5 c, which is a switching element of the presentinvention, such as a fast recovery diode, and a reverse currentprevention element 6 c, which is a reverse current prevention element ofthe present invention. The other configurations are the same as that ofEmbodiment 1. The same signs will be given to the same configurations.

Such a configuration allows the input current, which is an addition ofcurrents flowing through each step-up reactor 4, to have much smallercurrent ripple to further improve the harmonics current suppressioneffect.

The current flowing through the step-up reactor 4, switching element 5,reverse current prevention element 6 of each step-up converter 3 becomesfurther smaller and elements having further smaller capacity can beselected.

FIG. 9 shows a case where the step-up converter 3 has three systems,however, the present invention is not limited thereto. The step-upconverter 3 may be connected for an arbitrary number (N) that is threesystems or more in parallel.

As explained in the above Embodiment 1, the input current is theaddition of currents flowing through each step-up reactor 4. Forexample, when N systems of the step-up converter are connected inparallel, the current ripple of the input current becomes minimum at360/N degrees. Thereby, the current ripple frequency of the inputcurrent becomes N times of the switching frequency.

Then, the current ripple of the input current may cause noises at thefrequencies which is N times of the switching frequency. Thereby, bycontrolling the phase difference of the current flowing through eachstep-up reactor to be made to change only for several times in thevicinity of 360/N, components of N times of the switching frequency canbe reduced and noises can be suppressed.

The change of the phase difference can be changed at random by a phasedifference difference calculation section and the like within apredetermined area like the above Embodiment 1.

The larger the number of the system of the step-up converter 3, thesmaller the current ripple of the input current. Accordingly, theharmonics components suppression effect of the input current can beimproved. A noise filter can be made small.

The current flowing through the step-up reactor 4, switching element 5,reverse current prevention element 6 can be made smaller and elementshaving much smaller capacity can be selected.

The mode of the current flowing through the step-up reactor 4 can beswitched into any of the continuous mode, the critical mode, or thediscontinuous mode based on trade-off between the number (N) of thesystem of the step-up converter 3 and the current mode. For example, avariety of configurations are possible such as a configuration operableunder the continuous mode when focusing on the suppression effect of theharmonics components, the configuration operable under the critical modewhen focusing on small and light-weighted type, a configuration operableunder the discontinuous mode when focusing on low loss.

Embodiment 4

FIG. 10 is a configuration diagram of the converter circuit according toEmbodiment 4 of the present invention. in FIG. 10, the rectifier 2 thatrectifies the AC voltage of the commercial power supply 1 is configuredto bridge-connect four rectifying diodes 2 a to 2 d. To the output ofthe rectifier 2, the step-up converter 3 a and the step-up converter 3 bare connected in parallel.

The step-up converter 3 a is composed of the step-up reactor 4 a,switching element 5 a such as an IGBT, the reverse current preventionelement 6 a such as a fast recovery diode.

The step-up converter 3 b is also composed of the step-up reactor 4 b,the switching element 5 b such as an IGBT, the reverse currentprevention element 6 bv such as a fast recovery diode.

The switching elements 5 a and 5 b are controlled by the switchingcontrol means 7 to boost the output of the rectifier 2. The inductance Lof the step-up reactors 4 a and 4 b employs the values defined by theabove formula 1 when the current flowing therethrough is made to be thecritical mode or discontinuous mode like the above-mentioned Embodiment1.

Switching elements 5 a and switching elements 5 b are provided with aFWD connected in inverse-parallel, respectively. The diode prevents theswitching element 5 from being broken caused by a surge generated whenthe switching element 5 turns off.

In the present embodiment, the step-up converter 3 is not limited, butany switching converter can be applied such as a step-up converter, astep-down converter, a step-up/step-down converter.

The output of the step-up converter 3 a and the step-up converter 3 b issmoothed by the smoothing capacitor 8. To the output of the step-upconverters 3 a and 3 b, a load (not shown) is connected and the outputof the smoothed step-up converters 3 a and 3 b is applied.

To the output side of the step-up converter 3 a, opening and closingmeans 9 a is provided composed of a switching element that opens andcloses the output of the step-up converter 3 a. To the output side ofthe step-up converter 3 b, opening and closing means 9 b is providedcomposed of a switching element that opens and closes the output of thestep-up converter 3 b. The opening and closing control means 40 isprovided that controls the opening and closing of the opening andclosing means 9 a and 9 b.

Descriptions will be given to the behavior and operation of theconverter circuit configured above as follows.

If both opening and closing means 9 a and 9 b are on state, the circuitconfiguration is the same as that of the above Embodiment 1. The ACvoltage of the commercial power supply 1 is rectified by the rectifier 2like the above Embodiment 1. The output of the rectifier 2 is branchedinto two current paths by the step-up converters 3 a and 3 b connectedin parallel. The branched current flows into the step-up reactors 4 aand 4 b, switching of the switching elements 5 a and 5 b beingcontrolled by the switching control means 7, and the output of therectifier 2 being boosted. The switching control means 7 controlsswitching of the switching elements 5 a and 5 b to control the currentmode and phase difference of the current flowing through the step-upreactors 4 a and 4 b. The switching operation is the same as that of theabove Embodiment 1.

When both opening and closing means 9 a and 9 b are on-state, the sameeffect as the above Embodiment 1 can be obtained.

Next, descriptions will be given to switching operation of useconditions of the step-up converters 3 a and 3 b by the opening andclosing means 9 a and 9 b.

As shown in FIG. 10, the converter circuit of the present embodiment isprovided with the opening and closing means 9 a and 9 b controlled bythe opening and closing control means 40.

The opening and closing control means 40 opens and closes at leasteither of the opening and closing means 9 a or 9 b based on apredetermined condition to operate both or either of the step-upconverters 3 a or 3 b. That is, when the opening and closing means 9 ais made to on and the opening and closing means 9 b is made to off, thestep-up converter 3 a can be made to be a used state and the step-upconverter 3 b can be made to be a stop state. Alternatively, when theopening and closing means 9 a is made to off and the opening and closingmeans 9 b is made to on, the step-up converter 3 a can be made to be thestop state and the step-up converter 3 b can be made to be the usedstate.

Switching of use conditions of the step-up converters 3 a and 3 b by theopening and closing means 9 a and 9 b (hereinafter, simply referred toas “use conditions”) is performed by providing a threshold value withthe input current level, the switching frequency, the circuitefficiency, the output power, and so on. Descriptions will be given tothe predetermined condition to switch the use conditions and concreteexamples thereof as follows.

Firstly, as the predetermined condition for switching the useconditions, the operation based on the input current will be explained.

In addition to the configuration of the above-mentioned FIG. 10, currentdetection means 20 is provided that detects the input current input tothe step-up converters 3 a and 3 b like the above-mentioned Embodiment 2(FIG. 5).

The opening and closing control means 40 switches on-off of the openingand closing means 9 a and 9 b based on the magnitude (level) of theinput current detected by the current detection means 20.

The opening and closing control means 40 is set with 30% of the peakvalue of the input current being the threshold, for example. When themagnitude (level) of the detected input current is equal to or largerthan the threshold, both opening and closing means 9 a and 9 b are madeto be on and both step-up converters 3 a and 3 b are made to be in theused state.

On the other hand, when the magnitude (level) of the detected inputcurrent is less than the threshold, either the opening and closing means9 a or 9 b is made to be on and the other off, and either step-upconverters 3 a or 3 b is made to be in the used state.

Through the above-mentioned operations, in the vicinity of the peakhaving a large input current, since the input current is divided intothe route of the step-up converter 3 a and the route of 3 b by makingboth of them to be a used condition, the current flowing through thecomponents of each step-up converter 3 can be suppressed.

In the vicinity of the zero cross having a small input current, bymaking either the step-up converter 3 a or 3 b to be the used condition,no operation loss occurs in the step-up converter 3 under the stopstate, allowing to reduce circuit loss.

Next, descriptions will given to operations based on the switchingfrequency as the predetermined condition for switching the useconditions.

As shown in Embodiment 2 (FIG. 6), the switching frequency cannot bemade to be constant during the operation in the critical mode. While theswitching frequency is low in the vicinity of the peak of the inputcurrent, it is high in the vicinity of the zero cross. Thereby, theopening and closing control means 40 switches on-off of the opening andclosing means 9 a and 9 b based on the switching frequency of theswitching element 5.

In the opening and closing control means 40, a predetermined frequencyis set as a threshold. Into the opening and closing control means 40,information on the switching frequency is input from the switchingcontrol means 7. If the switching frequency is less than the threshold,both opening and closing means 9 a and 9 b becomes on and both step-upconverters are made to be the used state.

On the other hand, if the switching frequency is equal to or more thanthe threshold, either opening and closing means 9 a or 9 b becomes onand the other off, and either step-up converter 3 a or 3 b becomes theused state.

Through the above-mentioned operations, in the region having a lowswitching frequency, since the input current is divided into the routeof the step-up converter 3 a and the route of 3 b by making both of themto be a used state, the current flowing through the components of eachstep-up converter 3 can be suppressed.

In the region where the switching frequency is high, by making eitherthe step-up converter 3 a or 3 b to be a used state, no operation lossoccurs in the step-up converter 3 under the stop state, allowing toreduce circuit loss.

If the threshold of the switching frequency set at the opening andclosing control means 40 is set according to the specification of theswitching element 5, for example, the switching element 5 can beprevented from breakdown and used under more favorable environment.

Next, descriptions will be given to operations based on the outputvoltage as the predetermined condition for switching the use conditions.

During the operation in the critical mode, regarding the output power,the higher the load, the lower the switching frequency. Therefore, theopening and closing control means 40 switches on-off of the opening andclosing means 9 a and 9 b based on the output power.

In addition to the above-mentioned configuration of FIG. 10, likeEmbodiment 2 (FIG. 8) the above, the output power detection means 30 isprovided that detects the output power of the step-up converters 3 a and3 b.

The opening and closing control means 40 switches on-off of the openingand closing means 9 a and 9 b based on the output power detected by theoutput power detection means 30.

With the opening and closing control means 40, a predetermined outputpower is set as a threshold in advance. When the detected output poweris equal to or larger than the threshold, both opening and closing means9 a and 9 b are turned on and both step-up converters 3 a and 3 b aremade to be the used state.

On the other hand, when the detected output power is less than thethreshold, either opening and closing means 9 a or 9 b is turned on andthe other off, and either step-up converter 3 a or 3 b is made to be theused state.

Through the above-mentioned operations, in the case of the high load,since the input current is divided into the route of the step-upconverter 3 a and the route of 3 b by making both of them to be the usedstate, the current flowing through the components of each step-upconverter 3 can be suppressed.

In the case of the low load, by making either the step-up converter 3 aor 3 b to be the used state, no operation loss occurs in the step-upconverter 3 under the stop state, allowing to reduce circuit loss.

While the current mode is frequently switched within a power sourcecycle in the case where a threshold is provided for the above-mentionedinput current and the switching frequency, the frequency of on-offswitching is low for the opening and closing means 9 a and 9 b when thecurrent mode is switched based on the output power like the above,allowing to perform control with a simpler program.

Next, descriptions will be given to operations based on the circuitefficiency as the predetermined condition for switching the usecondition.

In the low load area, the circuit efficiency increases as the outputpower increases, however, in the high load area, the circuit efficiencysometimes decreases. Therefore, the opening and closing control means 40switches on-off of the opening and closing means 9 a and 9 b based onthe circuit efficiency.

In addition to the above-mentioned configuration of FIG. 10, the currentdetection means 20 and the output power detection means 30 are provided.With the opening and closing control means 40, a predetermined circuitefficiency value is set as a threshold in advance.

The opening and closing control means 40 obtains the circuit efficiencybased on the detected input current and the output power. When theobtained circuit efficiency value is less than the threshold, eitheropening and closing means 9 a or 9 b is turned on, the other off, andeither step-up converter 3 a or 3 b is made to be the used state. On theother hand, when the circuit efficiency value is equal to or larger thanthe threshold, both opening and closing means 9 a and 9 b are turned onand both step-up converters 3 a and 3 b are made to be the used state.

Through the above-mentioned operations, by making either step-upconverter 3 a or 3 b to be in the used state when the circuit efficiencyis decreased, no operation loss occurs in the step-up converter 3 underthe stop state, allowing to improve the circuit efficiency.

Next, as the predetermined condition for switching the use condition,operations will be explained based on the output voltage, the outputvoltage command, or the changed values of the output voltage command.

When changing the output voltage command against the step-up converter3, the current ripple of the input current changes as well. Thereby, theopening and closing control means 40 switches on-off of the opening andclosing means 9 a and 9 b based on the output voltage, the outputvoltage command, or the changed value of the output voltage command.

To the switching control means 7, the output voltage command that setsthe output voltage of the step-up converter 3 is input. The switchingcontrol means 7 controls the switching element 5 according to the outputvoltage command to set the output voltage of the step-up converter 3.

To the opening and closing control means 40, information on the outputvoltage command is input. To the opening and closing control means 40,the predetermined value or range is set in advance as the threshold, forwhich the current ripple becomes large against the output voltage, theoutput voltage command, or the changed values of the output voltagecommand.

The opening and closing control means 40 turns both opening and closingmeans 9 a and 9 b on and makes both step-up converters 3 a and 3 b to beused state when the output voltage, the output voltage command, or thechanged value of the output voltage command is the predetermined valueor in the area.

Through the above-mentioned operations, by making both step-upconverters 3 a and 3 b to be the used state, the current ripple of theinput current can be made small and harmonic components can besuppressed when the output voltage command changes and the currentripple increases.

Next, descriptions will be given to operations of switching by anarbitrary period as the predetermined condition for switching the usecondition.

If the use condition is maintained for both or either step-up converter3 a or 3 b, the temperature increases of each element constituting thestep-up converter 3. Thereby, the opening and closing control means 40switches on-off of the opening and closing means 9 a and 9 b at anarbitrary period to switch the used state and the stop state of thestep-up converters 3 a and 3 b at an arbitrary period.

Through such operations, temperature rise in the step-up reactor 4,switching element 5, and reverse current prevention element 6constituting the step-up converter 3 can be suppressed and the convertercircuit can be more efficiently operated.

By suppressing temperature rise in each element, breakdown of elementsdue to excess operation temperature can be prevented and long term usagebecomes possible.

In Embodiment 4, by adjusting the phase difference of the currentflowing through the step-up reactors 4 a and 4 b to be 180 degrees or arandom value centering around 181 degrees, harmonics of the inputcurrent and noise vibrations caused by the current ripple can besuppressed.

In Embodiment 4, the case where the step-up converter 3 has two systemsis explained. However, the present invention is not limited thereto, buta plurality of systems may be connected in parallel for the step-upconverter 3 as shown in FIG. 11, for example. Through such aconfiguration, the same effect as Embodiment 3 can be obtained.

Embodiment 5

In the above Embodiment 2, the current mode flowing through the step-upreactors 4 is switched based on the predetermined condition. InEmbodiment 4, the use condition of the step-up converters 3 a and 3 b isswitched based on the predetermined condition. In Embodiment 5, theswitching of the use condition of the step-up converters 3 a and 3 b andthe switching of the current mode flowing through the step-up reactors 4are performed simultaneously based on the predetermined condition.

Descriptions will be given to the predetermined condition to switch theused condition and the current mode and concrete examples thereof asfollows. The configuration of the converter circuit in Embodiment 5 isthe same as that in Embodiment 4.

Firstly, as the predetermined condition for switching the use conditionand the current mode, operations will be explained based on the inputcurrent.

Like the above Embodiment 4, when the magnitude (level) of the inputcurrent detected by the current detection means 20 is equal to or largerthan the threshold, the opening and closing control means 40 turns bothopening and closing means 9 a and 9 b on and makes both step-upconverters 3 a and 3 b to be used state. The switching control means 7controls the switching of the switching element 5 so that the currentmode flowing through the step-up reactor 4 is made to be the criticalmode or the discontinuous mode.

When the magnitude (level) of the detected input current is less thanthe threshold, the opening and closing control means 40 turns eitheropening and closing means 9 a or 9 b on and the other off to make eitherstep-up converter 3 a or 3 b to be used state. The switching controlmeans 7 controls the switching of the switching element 5 so that thecurrent mode flowing through the step-up reactor 4 is made to be thecontinuous mode.

Through such operations, in the area near the peak where the inputcurrent is large, by making both step-up converters 3 a and 3 b to beused state and making the current mode to be the critical mode or thediscontinuous mode, not only the current flowing through components ofeach step-up converter 3 can be suppressed, but also the current rippleflowing through the step-up reactor 4 can be made large, and theswitching loss can be reduced because of the decrease in the switchingfrequency.

In the area near the zero cross where the input current is small, bymaking either the step-up converter 3 a or 3 b is made to be the usedstate and the current to be the continuous mode, no operation lossoccurs in the step-up converter 3 under the stop state, allowing thecircuit loss to be reduced, and at the same time, the ripple of theinput current is made small, allowing the harmonics component to besuppressed.

Next, descriptions will be given to operations based on the switchingfrequency as the predetermined condition for switching the use conditionand the current mode.

Like the above Embodiment 4, when the switching frequency is less thanthe threshold, the opening and closing control means 40 turns bothopening and closing means 9 a and 9 b on and makes both step-upconverters 3 a and 3 b to be used state. The switching control means 7controls the switching of the switching element 5 so that the currentmode flowing through the step-up reactor 4 to be the critical mode orthe discontinuous mode.

When the switching frequency is equal to or larger than the threshold,the opening and closing control means 40 turns either opening andclosing means 9 a or 9 b on and the other off and makes either step-upconverter 3 a or 3 b to be used state. The switching control means 7controls the switching of the switching element 5 so that the currentflowing through the step-up reactor 4 to be the continuous mode.

Through such operations, in the area where the switching frequency islow, by making both step-up converters 3 a and 3 b to be used state andmaking the current mode to be the critical mode or the discontinuousmode, the current flowing through components of each step-up converter 3can be suppressed, and at the same time, the current ripple flowingthrough the step-up reactor 4 can be made large, allowing the switchingloss to be reduced because of the decrease in the switching frequency.

In the area where switching frequency is high, by making either step-upconverter 3 a or 3 b to be the used state, and making the current to bethe continuous mode, no operation loss occurs in the step-up converter 3under the stop state, the circuit loss being reduced, the ripple of theinput current being made small, allowing the harmonics components to besuppressed.

Next, descriptions will be given to operations based on the outputvoltage as the predetermined condition for switching the use conditionand the current mode.

Like the above Embodiment 4, when the magnitude of the output powerdetected by the output power detection means 30 is equal to or largerthan the threshold, the opening and closing control means 40 turns bothopening and closing means 9 a and 9 b on and makes both step-upconverters 3 a and 3 b to be used state. The switching control means 7controls the switching of the switching element 5 so that the currentmode flowing through the step-up reactor 4 to be the critical mode orthe discontinuous mode.

When the magnitude of the detected output power is less than thethreshold, the opening and closing control means 40 turns either openingand closing means 9 a or 9 b on and the other off and makes eitherstep-up converter 3 a or 3 b to be used state. The switching controlmeans 7 controls the switching of the switching element 5 so that thecurrent mode flowing through the step-up reactor 4 to be the criticalmode or the discontinuous mode.

Through such operations, in the case of high load, by making bothstep-up converters 3 a and 3 b to be used state, the current flowingthrough components of each step-up converter 3 can be suppressed, and bymaking the current to be the critical mode or the discontinuous mode,the switching loss can be reduced because of the decrease in theswitching frequency.

In the case of low load, by making either step-up converter 3 a or 3 bto be the used state, and making the current to be the continuous mode,no operation loss occurs in the step-up converter 3 under the stopstate, loss of the circuit being reduced, the ripple of the inputcurrent being made small, allowing the harmonics components to besuppressed.

Next, descriptions will be given to operations based on the circuitefficiency as the predetermined condition for switching the usecondition and the current mode.

Like the above Embodiment 4, when the circuit efficiency is less thanthe threshold, the opening and closing control means 40 turns eitheropening and closing means 9 a or 9 b on and the other off, and makeseither step-up converter 3 a or 3 b to be used state. The switchingcontrol means 7 switches the current flowing through the step-up reactor4 to the discontinuous mode when it is in the critical mode and viceversa.

Through such operations, in the case where the circuit efficiencydecreases, by making either step-up converter 3 a or 3 b to be usedstate, no operation loss occurs in the step-up converter 3 under thestop state, and the circuit efficiency can be improved. When the circuitefficiency decreases, the circuit efficiency can be improved by reducingthe switching frequency to decrease the switching loss.

Next, descriptions will be given to operations based on the outputvoltage, the output voltage command, or the changed values of the outputvoltage command as the predetermined condition for switching the usecondition and the current mode.

Like the above Embodiment 4, to the switching control means 7, theoutput voltage command is input that sets the output voltage of thestep-up converter 3. Based on the output voltage command, the switchingcontrol means 7 controls the switching element 5 to set the outputvoltage of the step-up converter 3.

When the output voltage, the output voltage command, or the changedvalues of the output voltage command are the predetermined value orrange where the current ripple becomes large, the opening and closingcontrol means 40 makes both opening and closing means 9 a and 9 b to beon and makes both step-up converter 3 a and 3 b in the used state. Theswitching control means 7 controls the switching of the switchingelement 5 so that the current flowing through the step-up reactor 4becomes the continuous mode.

Through such operations, when the current ripple increases because ofthe change in the output voltage command, the ripple of the inputcurrent can be made to be small and harmonics components can besuppressed by making both step-up converters 3 a and 3 b to be the usedstate and making the current mode to be the continuous mode.

In the above descriptions, according to the predetermined conditionssuch as the level of the input current, switching frequency, circuitefficiency, or output power, the use condition and the current mode areswitched. However, the current mode may be switched according to theopening closing conditions of the opening and closing means 9 a and 9 b.

That is, based on the opening closing conditions of the opening andclosing means 9 a and 9 b, the switching control means 7 may be adaptedto switch the current flowing through the step-up reactors 4 a and 4 binto any of the continuous mode, the critical mode, and thediscontinuous mode.

For example, when both opening and closing means 9 a and 9 b are onstate and both step-up converters 3 a and 3 b are in the used state, thecurrent flowing through the step-up reactor 4 a and 4 b is made to bethe critical mode or the discontinuous mode. On the other hand, wheneither opening and closing means 9 a or 9 b is on state and the otheroff state, and either step-up converter 3 a or 3 b is in the used state,the current flowing through the step-up reactor 4 under the used stateis made to be the continuous mode.

Through such operations, when both step-up converters 3 a and 3 b are inthe used state, by making the current to be the critical mode or thediscontinuous mode, the switching loss can be reduced. At the same time,since the input current becomes an addition of two current paths by thestep-up converters 3 a and 3 b and operates under the continuous mode,the ripple of the input current can be made small to suppress theharmonics components.

By making either step-up converter 3 a or 3 b in the used state andmaking the current to be the continuous mode, no operation loss occursin the step-up converter 3 under the stop state, and the loss in thecircuit can be reduced. Since the step-up converter 3 under the usedstate operates in the continuous mode, the ripple of the input currentcan be made small and harmonics components can be suppressed.

In Embodiment 5, like the above Embodiment 1, by adjusting the phasedifference of the current flowing through the step-up reactors 4 a and 4b to be 180 degrees or a random value centering therearound, harmonicscomponents of the input current and noises or vibrations caused by thecurrent ripple can be suppressed.

In Embodiment 5, descriptions are given to the case where the step-upconverter 3 includes two systems. However, the present invention is notlimited thereto, and a plurality system of the step-up converter 3 maybe connected in parallel like Embodiment 3. Through such aconfiguration, the same effect as the above Embodiment 3 can beobtained.

Embodiment 6

In Embodiment 6, an example of configuration is shown where a motordrive control apparatus is made to be an object load regarding theconverter circuit of the above Embodiments 1 to 5.

FIG. 12 is a configuration diagram of the motor drive control apparatusaccording to Embodiment 6 of the present invention.

In FIG. 12, the rectifier 2 that rectifies the AC voltage of thecommercial power supply 1 is constituted by four bridge-connectedrectifying diodes 2 a to 2 d. To the output of the rectifier 2, thestep-up converters 3 a and 3 b are connected in parallel.

The step-up converter 3 a is constituted by a step-up reactor 4 a, aswitching element 5 a such as an IGBT, and a reverse current preventionelement 6 a such as a fast recovery diode. The step-up converter 3 b isconstituted by the step-up reactor 4 b, the switching element 5 b suchas the IGBT, and the reverse current prevention element 6 b such as afast recovery diode, as well.

By switching control means 7, the switching of the switching elements 5a and 5 b is controlled and the output of the rectifier 2 is boosted.

An FRD is provided which is connected in inverse-parallel with theswitching elements 5 a and 5 b, respectively. The FRD prevents theswitching element 5 from breakdown by the surge that is generated whenthe switching element 5 turns off.

In the present embodiment, the step-up converter 3 is not limited, butany switching converter may be applied such as a step-up converter, astep-down converter, a step-up/step-down converter.

The output of the step-up converters 3 a and 3 b is smoothed by thesmoothing capacitor 8. A load 10 is connected with the output of thestep-up converters 3 a and 3 b and the smoothed output of the step-upconverters 3 a and 3 b is applied.

The load 10 is constituted by an inverter circuit 11 that converts theoutput of the step-up converters 3 a and 3 b into AC voltage and a motor12 connected with the inverter circuit 11.

The inverter circuit 11 is constituted by bridge-connected switchingelements 11 a to 11 f. In each switching element 11 a to 11 f, a fastrecovery diode is built-in in inverse-parallel. The built-in fastrecovery diode functions to flow a free-wheeling current when theswitching elements 11 a to 11 f turn off. The inverter circuit 11 issubjected to PWM control, for example, by the inverter drive means 50 toconvert input DC voltage into AC voltage having arbitrary voltages andfrequencies to drive the motor 12.

The motor drive control apparatus is constituted by the convertercircuit, the inverter circuit 11, and inverter drive means 50.

In FIG. 12, descriptions are given to a case where the load 10 composedof the inverter circuit 11 and the motor 12 is provided with theconverter circuit of Embodiment 1. However, the present invention is notlimited thereto, but the load 10 composed of the inverter circuit 11 andthe motor 12 may be provided with any configuration of the aboveEmbodiments 1 to 5.

It goes without saying that the same effect as the above Embodiments 1to 5 can be obtained by operating the motor 12 with such aconfiguration.

Embodiment 7

FIG. 13 is a configuration diagram of an air-conditioner according toEmbodiment 7 of the present invention.

In FIG. 13, an air-conditioner according to the present embodimentincludes an outdoor unit 310 and an indoor unit 320. The outdoor unit310 includes a refrigerant compressor 311 that is connected with arefrigerant circuit, not shown, and configures a refrigerant cycle and ablower 312 for the outdoor unit that blows in a heat exchanger, notshown. The refrigerant compressor 311 and the blower 312 for the outdoorunit are driven by a motor 12 that is controlled by the motor drivecontrol apparatus according to the above Embodiment 6. It goes withoutsaying that the same effect as the above Embodiments 1 to 6 can beobtained by operating the motor 12 with such a configuration.

Embodiment 8

FIG. 14 is a configuration diagram of a refrigerator according toEmbodiment 8 of the present invention.

As shown in FIG. 14, a refrigerator 400 includes a refrigerantcompressor 401 that configures a refrigeration cycle connected with arefrigeration circuit, not shown, and a cool air circulation blower 404that that sends cool air generated in a cooler 403 installed in acooling compartment 402 to refrigerating compartment, freezingcompartment, and the like. The refrigerant compressor 401 and the coolair circulation blower 404 are driven by the motor 12 that is controlledby the motor drive control apparatus according to the above Embodiment6. It goes without saying that the same effect as the above Embodiments1 to 6 can be obtained by operating the motor 12 with such aconfiguration.

Embodiment 9

In Embodiment 9, an example of configuration is shown when an inductionheating cooker is made to be an object load regarding the convertercircuit of the above Embodiments 1 to 5.

FIG. 15 is a configuration diagram of the induction heating cookeraccording to Embodiment 9 of the present invention.

In FIG. 15, the rectifier 2 that rectifies the AC voltage of thecommercial power supply 1 is constituted by four bridge-connectedrectifying diodes 2 a to 2 d. To the output of the rectifier 2, thestep-up converters 3 a and 3 b are connected in parallel.

The step-up converter 3 a is constituted by a step-up reactor 4 a, aswitching element 5 a such as an IGBT, and a reverse current preventionelement 6 a such as a fast recovery diode. The step-up converter 3 b isconstituted by the step-up reactor 4 b, the switching element 5 b suchas the IGBT, and the reverse current prevention element 6 b such as thefast recovery diode, as well.

By switching control means 7, the switching of the switching elements 5a and 5 b is controlled and the output of the rectifier 2 is boosted.

An FRD is provided which is connected in inverse-parallel with theswitching elements 5 a and 5 b, respectively. The FRD prevents theswitching element 5 from breakdown by the surge that is generated whenthe switching element 5 turns off.

In the present embodiment, the step-up converter 3 is not limited, butany switching converter may be applied such as a step-up converter, astep-down converter, a step-up/step-down converter.

The output of the step-up converters 3 a and 3 b is smoothed by thesmoothing capacitor 8. A load 10 is connected with the output of thestep-up converters 3 a and 3 b and the smoothed output of the step-upconverters 3 a and 3 b is applied.

The load 10 is constituted by an inverter circuit 11 that converts theoutput of the step-up converters 3 a and 3 b into AC voltage and a loadcircuit 13 connected with the inverter circuit 11.

The inverter circuit 11 is constituted by bridge-connecting switchingelements 11 a to 11 f.

The inverter circuit 11 is driven by the inverter drive means 50 toconvert the DC voltage smoothed by the smoothing capacitor 8.

To the output point of the inverter circuit 11, a load circuit 13composed of an induction heating coil 14 and a resonance capacitor 15 isconnected. A high-frequency voltage converted by the inverter circuit 11is applied to the load circuit 13. Thereby, an object to be heated (notshown) mounted on the induction heating cooker is subjected to inductionheating.

In FIG. 15, a case is shown where the load 10 composed of the invertercircuit 11 and the load circuit 13 is provided with the convertercircuit of the above Embodiment 1. However, the present invention is notlimited thereto, but the load 10 composed of the inverter circuit 11 andthe load circuit 13 may be provided with any configuration of the aboveEmbodiments 1 to 5.

It goes without saying that the same effect as the above Embodiments 1to 5 can be obtained by operating the load circuit 13 by such aninduction heating cooker.

For example, as shown in FIG. 12 or 15, when the inverter circuit 11 isconnected as the load, since a large-capacity switching element used forthe switching converter is usually required, it is difficult to beshared with the switching element used for the inverter circuit.

According to Embodiments 1 to 9, the switching elements can be sharedand cost reduction is made possible eventually by selecting the numberof the step-up converters which can be configured by the switchingelements 5 used in the converter circuit and the switching elements 11 ato 11 f used in the inverter circuit 11 having the same capacity.

In the above, descriptions are given to embodiments of the presentinvention. However, the present invention is not limited thereto, but itgoes without saying that it is subject to change without being limitedby embodiments and without departing from the spirit and scope of theinvention such as to employ a three-phase power source instead of thesingle phase for the commercial power supply 1.

1-8. (canceled)
 9. A converter circuit, comprising: a rectifier thatrectifies an AC voltage; at least a converter section that is connectedwith an output of said rectifier and has a reactor, a switching element,and a reverse current prevention element; switching control means thatcontrols said switching element; and a smoothing capacitor that isprovided at an output of said converter section, wherein at apredetermined value or in a predetermined range of an output voltage ofsaid converter section, a current mode of a current flowing through saidreactor is controlled by said switching control means and is one of atleast two modes among a critical mode, a discontinuous mode, and acontinuous mode.
 10. The converter circuit of claim 9, furthercomprising: one or more converter sections that are connected with theoutput of said rectifier, each of the one or more converter sections hasa reactor, a switching element, and a reverse current preventionelement, and each of the one or more converter sections is connectedwith said at least one converter section in parallel.
 11. The convertercircuit of claim 10, wherein said switching control means controlsswitching of said switching element and said switching element in eachof the one or more converter sections so as to create a predeterminedphase difference in the current flowing through said reactor and saidreactor in each of the one or more converter sections.
 12. The convertercircuit of claim 11, wherein said switching control means controlsswitching of said switching element and said switching element in eachof the one or more converter sections so that the phase difference ofthe currents flowing through said reactor and said reactor in each ofthe one or more converter sections randomly varies within apredetermined range.
 13. A motor drive control apparatus, comprising:the converter circuit of claim 9; an inverter circuit that converts a DCoutput voltage of said converter circuit to an AC voltage; and inverterdrive means that drives said inverter circuit.
 14. An air-conditioner,comprising: the motor drive control apparatus of claim 13; and a motorthat is driven by said motor drive control apparatus.
 15. Arefrigerator, comprising: the motor drive control apparatus of claim 13;and a motor that is driven by said motor drive control apparatus.